How Do You Write a Data Structure in Python?


Larry Thompson

How Do You Write a Data Structure in Python?

Python is a versatile programming language that offers several built-in data structures to efficiently store and manipulate data. However, there may come a time when you need to create your own custom data structure to meet specific requirements.

In this tutorial, we will explore the process of writing a data structure in Python from scratch.

Defining the Data Structure

To begin, let’s define the characteristics and functionality of our custom data structure. Think about what kind of data it will store and what operations it should support.

This will help us determine the underlying implementation and methods needed.

Once you have a clear understanding of your requirements, you can start implementing the actual class for your data structure. In Python, classes are used to define objects with their attributes and behavior.

Example: Creating a Stack

Let’s create an example data structure called Stack, which follows the Last-In-First-Out (LIFO) principle. It should support two main operations: push (to add an element) and pop (to remove the most recently added element).

class Stack:
    def __init__(self):
        self.items = []

    def push(self, item):

    def pop(self):
        if not self.is_empty():
            return self.pop()

In this example, we define a class called “Stack” with an empty list as its attribute “items”. The “__init__” method initializes an instance of the class with an empty stack.

The “push” method takes an item as input and appends it to the “items” list using the append() function. This operation adds the item to the top of the stack.

The “pop” method checks if the stack is not empty using the “is_empty” helper method (which we will define later). If it’s not empty, it removes and returns the most recently added item from the “items” list using the pop() function.

Implementing Additional Methods

Depending on your data structure’s requirements, you may need to implement additional methods. For example, our Stack data structure would benefit from having a method to check if it is empty.

class Stack:
    # previous code..

    def is_empty(self):
        return len(self.items) == 0

In this case, we introduce an “is_empty” method that returns True if the length of the “items” list is 0, indicating an empty stack.

Testing Your Data Structure

Once you have implemented your custom data structure, it’s essential to test its functionality and ensure it behaves as expected. You can create test cases and verify that all operations work correctly.

This step helps identify and fix any potential issues before using your data structure in production code.

Example: Testing Our Stack Data Structure

stack = Stack()

print(stack.pop())  # Output: 3
print(stack.pop())  # Output: 2
print(stack.is_empty())  # Output: False

In this example, we create a new instance of our Stack class called “stack”. We push three items onto the stack and then pop two items, printing the results.

Finally, we check if the stack is empty using the “is_empty” method.


Congratulations! You have successfully written a custom data structure in Python.

By defining the characteristics and functionality of your data structure, implementing the necessary methods, and thoroughly testing its functionality, you can create powerful and efficient data structures tailored to your specific needs.

Remember to leverage Python’s built-in data structures whenever possible, as they are optimized for various use cases. However, knowing how to create your own data structures will enable you to solve unique problems and gain a deeper understanding of programming concepts.

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